T cell receptor binding kinetics required for T cell activation depend on the density of cognate ligand on the antigen-presenting cell

Dual T cell receptor/chimeric antigen receptor engineered NK-92 cells targeting the HPV16 E6 oncoprotein and the tumor-associated antigen L1CAM exhibit enhanced cytotoxicity and specificity against tumor cells

The human papillomavirus type 16 (HPV16) causes a large fraction of genital and oropharyngeal carcinomas. To maintain the transformed state, the tumor cells must continuously synthesize the E6 and E7 viral oncoproteins, which makes them tumor-specific antigens. Indeed, specific T cell responses against them have been well documented and CD8+ T cells engineered to express T cell receptors (TCRs) that recognize epitopes of E6 or E7 have been tested in clinical studies with promising results, yet with limited clinical success. Using CD8+ T cells from peripheral blood of healthy donors, we have identified two novel TCRs reactive to an unexplored E618-26 epitope. These TCRs showed limited standalone cytotoxicity against E618-26-HLA-A*02:01-presenting tumor cells. However, a single-signaling domain chimeric antigen receptor (ssdCAR) targeting L1CAM, a cell adhesion protein frequently overexpressed in HPV16-induced cancer, prompted a synergistic effect that significantly enhanced the cytotoxic capacity of NK-92/CD3/CD8 cells armored with both TCR and ssdCAR when both receptors simultaneously engaged their respective targets, as shown by live microscopy of 2-D and 3-D co-cultures. Thus, virus-specific TCRs from the CD8+ T cell repertoire of healthy donors can be combined with a suitable ssdCAR to enhance the cytotoxic capacity of the effector cells and, indirectly, their specificity.

Force-Induced Site-Specific Enzymatic Cleavage Probes Reveal That Serial Mechanical Engagement Boosts T Cell Activation

The T cell membrane is studded with >104 T cell receptors (TCRs) that are used to scan target cells to identify short peptide fragments associated with viral infection or cancerous mutation. These peptides are presented as peptide-major-histocompatibility complexes (pMHCs) on the surface of virtually all nucleated cells. The TCR-pMHC complex forms at cell-cell junctions, is highly transient, and experiences mechanical forces. An important question in this area pertains to the role of the force duration in immune activation. Herein, we report the development of force probes that autonomously terminate tension within a time window following mechanical triggering. Force-induced site-specific enzymatic cleavage (FUSE) probes tune the tension duration by controlling the rate of a force-triggered endonuclease hydrolysis reaction. This new capability provides a method to study how the accumulated force duration contributes to T cell activation. We screened DNA sequences and identified FUSE probes that disrupt mechanical interactions with F > 7.1 piconewtons (pN) between TCRs and pMHCs. This rate of disruption, or force lifetime (τF), is tunable from tens of minutes down to 1.9 min. T cells challenged with FUSE probes with F > 7.1 pN presenting cognate antigens showed up to a 23% decrease in markers of early activation. FUSE probes with F > 17.0 pN showed weaker influence on T cell triggering further showing that TCR-pMHC with F > 17.0 pN are less frequent compared to F > 7.1 pN. Taken together, FUSE probes allow a new strategy to investigate the role of force dynamics in mechanotransduction broadly and specifically suggest a model of serial mechanical engagement boosting TCR activation.

How persistent infection overcomes peripheral tolerance mechanisms to cause T cell-mediated autoimmune disease

T cells help orchestrate immune responses to pathogens, and their aberrant regulation can trigger autoimmunity. Recent studies highlight that a threshold number of T cells (a quorum) must be activated in a tissue to mount a functional immune response. These collective effects allow the T cell repertoire to respond to pathogens while suppressing autoimmunity due to circulating autoreactive T cells. Our computational studies show that increasing numbers of pathogenic peptides targeted by T cells during persistent or severe viral infections increase the probability of activating T cells that are weakly reactive to self-antigens (molecular mimicry). These T cells are easily re-activated by the self-antigens and contribute to exceeding the quorum threshold required to mount autoimmune responses. Rare peptides that activate many T cells are sampled more readily during severe/persistent infections than in acute infections, which amplifies these effects. Experiments in mice to test predictions from these mechanistic insights are suggested.

Tuning the potency and selectivity of ImmTAC molecules by affinity modulation

T-cell-engaging bispecifics have great clinical potential for the treatment of cancer and infectious diseases. The binding affinity and kinetics of a bispecific molecule for both target and T-cell CD3 have substantial effects on potency and specificity, but the rules governing these relationships are not fully understood. Using immune mobilizing monoclonal TCRs against cancer (ImmTAC) molecules as a model, we explored the impact of altering affinity for target and CD3 on the potency and specificity of the redirected T-cell response. This class of bispecifics binds specific target peptides presented by human leukocyte antigen on the cell surface via an affinity-enhanced T-cell receptor and can redirect T-cell activation with an anti-CD3 effector moiety. The data reveal that combining a strong affinity TCR with an intermediate affinity anti-CD3 results in optimal T-cell activation, while strong affinity of both targeting and effector domains significantly reduces maximum cytokine release. Moreover, by optimizing the affinity of both parts of the molecule, it is possible to improve the selectivity. These results could be effectively modelled based on kinetic proofreading with limited signalling. This model explained the experimental observation that strong binding at both ends of the molecules leads to reduced activity, through very stable target-bispecific-effector complexes leading to CD3 entering a non-signalling dark state. These findings have important implications for the design of anti-CD3-based bispecifics with optimal biophysical parameters for both activity and specificity.

Genetically engineered CD80-pMHC-harboring extracellular vesicles for antigen-specific CD4+ T-cell engagement

The identification of low-frequency antigen-specific CD4+ T cells is crucial for effective immunomonitoring across various diseases. However, this task still encounters experimental challenges necessitating the implementation of enrichment procedures. While existing antigen-specific expansion technologies predominantly concentrate on the enrichment of CD8+ T cells, advancements in methods targeting CD4+ T cells have been limited. In this study, we report a technique that harnesses antigen-presenting extracellular vesicles (EVs) for stimulation and expansion of antigen-specific CD4+ T cells. EVs are derived from a genetically modified HeLa cell line designed to emulate professional antigen-presenting cells (APCs) by expressing key costimulatory molecules CD80 and specific peptide-MHC-II complexes (pMHCs). Our results demonstrate the beneficial potent stimulatory capacity of EVs in activating both immortalized and isolated human CD4+ T cells from peripheral blood mononuclear cells (PBMCs). Our technique successfully expands low-frequency influenza-specific CD4+ T cells from healthy individuals. In summary, the elaborated methodology represents a streamlined and efficient approach for the detection and expansion of antigen-specific CD4+ T cells, presenting a valuable alternative to existing antigen-specific T-cell expansion protocols.

A photo-activable nano-agonist for the two-signal model of T cell in vivo activation

The two-signal model of T cell activation has helped shape our understanding of the adaptive immune response for over four decades. According to the model, activation of T cells requires a stimulus through the T cell receptor/CD3 complex (signal 1) and a costimulatory signal 2. Stimulation of activatory signals via T cell agonists has thus emerged. However, for a robust T cell activation, it necessitates not only the presence of both signal 1 and signal 2, but also a high signaling strength. Herein, we report a photo-activable nano-agonist for the two-signal model of T cell in vivo activation. A UV-crosslinkable polymer is coated onto upconversion nanoparticles with satisfactory NIR-to-UV light conversion efficiency. Then dual signal molecules, i.e., signal 1 and signal 2, are conjugated to the polymer end to yield the photo-activable T cell nano-agonist. In melanoma and breast cancer models, photo-activable nano-agonist could bind onto corresponding activatory receptors on the surface of T cells, but has limited activity without the application of NIR light (absence of photo-crosslinking of receptors and consequently a poor signaling strength). While when the NIR light is switched on locally, T cells in tumor are remarkably activated and kill tumor cells effectively. Moreover, we do not observe any detectable toxicities related to the photo-activable nano-agonist. We believe with two activatory signals being simultaneously strengthened by local photo-switched crosslinking, T cells realize a robust and selective activation in tumor and, consequently contribute to an enhanced and safe tumor immunotherapy.

Force-induced site-specific enzymatic cleavage probes reveal that serial mechanical engagement boosts T cell activation

The surface of T cells is studded with T cell receptors (TCRs) that are used to scan target cells to identify peptide-major histocompatibility complexes (pMHCs) signatures of viral infection or cancerous mutation. It is now established that the TCR-pMHC complex is highly transient and experiences mechanical forces that augment the fidelity of T cell activation. An important question in this area pertains to the role of force duration in immune activation. Herein, we report the development of force probes that autonomously terminate tension within a time window following mechanical triggering. Force-induced site-specific enzymatic cleavage (FUSE) probes tune tension duration by controlling the rate of a force-triggered endonuclease hydrolysis reaction. This new capability provides a method to study how accumulated force duration contributes to T cell activation. We screened DNA sequences and identified FUSE probes that disrupt mechanical interactions with F >7.1 piconewtons (pN) between TCRs and pMHCs. Force lifetimes (τF) are tunable from tens of min down to 1.9 min. T cells challenged with FUSE probes presenting cognate antigens with τF of 1.9 min demonstrated dampened markers of early activation, thus demonstrating that repeated mechanical sampling boosts TCR activation. Repeated mechanical sampling F >7.1 pN was found to be particularly critical at lower pMHC antigen densities, wherein the T cell activation declined by 23% with τF of 1.9 min. FUSE probes with F >17.0 pN response showed weaker influence on T cell triggering further showing that TCR-pMHC with F >17.0 pN are less frequent compared to F >7.1 pN. Taken together, FUSE probes allow a new strategy to investigate the role of force dynamics in mechanotransduction broadly and specifically suggest a model of serial mechanical engagement in antigen recognition.

Defining and Studying B Cell Receptor and TCR Interactions

BCRs (Abs) and TCRs (or adaptive immune receptors [AIRs]) are the means by which the adaptive immune system recognizes foreign and self-antigens, playing an integral part in host defense, as well as the emergence of autoimmunity. Importantly, the interaction between AIRs and their cognate Ags defies a simple key-in-lock paradigm and is instead a complex many-to-many mapping between an individual's massively diverse AIR repertoire, and a similarly diverse antigenic space. Understanding how adaptive immunity balances specificity with epitopic coverage is a key challenge for the field, and terms such as broad specificity, cross-reactivity, and polyreactivity remain ill-defined and are used inconsistently. In this Immunology Notes and Resources article, a group of experimental, structural, and computational immunologists define commonly used terms associated with AIR binding, describe methodologies to study these binding modes, as well as highlight the implications of these different binding modes for therapeutic design.

The landscape of T cell antigens for cancer immunotherapy

The remarkable capacity of immunotherapies to induce durable regression in some patients with metastatic cancer relies heavily on T cell recognition of tumor-presented antigens. As checkpoint-blockade therapy has limited efficacy, tumor antigens have the potential to be exploited for complementary treatments, many of which are already in clinical trials. The surge of interest in this topic has led to the expansion of the tumor antigen landscape with the emergence of new antigen categories. Nonetheless, how different antigens compare in their ability to elicit efficient and safe clinical responses remains largely unknown. Here, we review known cancer peptide antigens, their attributes and the relevant clinical data and discuss future directions.

Theoretical quantification of the polyvalent binding of nanoparticles coated with peptide-major histocompatibility complex to T cell receptor-nanoclusters

Nanoparticles (NPs) coated with peptide-major histocompatibility complexes (pMHCs) can be used as a therapy to treat autoimmune diseases. They do so by inducing the differentiation and expansion of disease-suppressing T regulatory type 1 (Tr1) cells by binding to their T cell receptors (TCRs) expressed as TCR-nanoclusters (TCR_nc). Their efficacy can be controlled by adjusting NP size and number of pMHCs coated on them (referred to as valence). The binding of these NPs to TCR_nc on T cells is thus polyvalent and occurs at three levels: the TCR-pMHC, NP-TCR_nc and T cell levels. In this study, we explore how this polyvalent interaction is manifested and examine if it can facilitate T cell activation downstream. This is done by developing a multiscale biophysical model that takes into account the three levels of interactions and the geometrical complexity of the binding. Using the model, we quantify several key parameters associated with this interaction analytically and numerically, including the insertion probability that specifies the number of remaining pMHC binding sites in the contact area between T cells and NPs, the dwell time of interaction between NPs and TCR_nc, carrying capacity of TCR_nc, the distribution of covered and bound TCRs, and cooperativity in the binding of pMHCs within the contact area. The model was fit to previously published dose-response curves of interferon-γ obtained experimentally by stimulating a population of T cells with increasing concentrations of NPs at various valences and NP sizes. Exploring the parameter space of the model revealed that for an appropriate choice of the contact area angle, the model can produce moderate jumps between dose-response curves at low valences. This suggests that the geometry and kinetics of NP binding to TCR_nc can act in synergy to facilitate T cell activation.

Current Trends in Neoantigen-Based Cancer Vaccines

Cancer immunotherapies are treatments that use drugs or cells to activate patients’ own immune systems against cancer cells. Among them, cancer vaccines have recently been rapidly developed. Based on tumor-specific antigens referred to as neoantigens, these vaccines can be in various forms such as messenger (m)RNA and synthetic peptides to activate cytotoxic T cells and act with or without dendritic cells. Growing evidence suggests that neoantigen-based cancer vaccines possess a very promising future, yet the processes of immune recognition and activation to relay identification of a neoantigen through the histocompatibility complex (MHC) and T-cell receptor (TCR) remain unclear. Here, we describe features of neoantigens and the biological process of validating neoantigens, along with a discussion of recent progress in the scientific development and clinical applications of neoantigen-based cancer vaccines.

Dendritic cell-mimicking scaffolds for ex vivo T cell expansion

We propose an ex vivo T cell expansion system that mimics natural antigen-presenting cells (APCs) for adoptive cell therapy (ACT). Microfiber scaffolds coated with dendritic cell (DC) membrane replicate physicochemical properties of dendritic cells specific for T cell activation such as rapid recognition by T cells, long duration of T cell tethering, and DC-specific co-stimulatory cues. The DC membrane-coated scaffold is first surface-immobilized with T cell stimulatory ligands, anti-CD3 (αCD3) and anti-CD28 (αCD28) antibodies, followed by adsorption of releasable interleukin-2 (IL-2). The scaffolds present both surface and soluble cues to T cells ex vivo in the same way that these cues are presented by natural APCs in vivo. We demonstrate that the DC-mimicking scaffold promotes greater polyclonal expansion of primary human T cells as compared to αCD3/αCD28-functionalized Dynabead. More importantly, major histocompatibility complex molecules derived from the DC membrane of the scaffold allow antigen-specific T cell expansion with target cell-specific killing ability. In addition, most of the expanded T cells (∼97%) can be harvested from the scaffold by density gradient centrifugation. Overall, the DC-mimicking scaffold offers a scalable, modular, and customizable platform for rapid expansion of highly functional T cells for ACT.

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The scaffold mimics physicochemical properties of natural antigen-presenting cells.

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The scaffold presents T cell stimulatory cues as antigen-presenting cell does.

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This platform supports both polyclonal and antigen-specific T cell expansion.

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This platform offers a large-scale manufacturing system for adoptive cell therapy.

Structures of NF-κB p52 homodimer-DNA complexes rationalize binding mechanisms and transcription activation

The mammalian NF-κB p52:p52 homodimer together with its cofactor Bcl3 activates transcription of κB sites with a central G/C base pair (bp), while it is inactive toward κB sites with a central A/T bp. To understand the molecular basis for this unique property of p52, we have determined the crystal structures of recombinant human p52 protein in complex with a P-selectin(PSel)-κB DNA (5'-GGGGTGACCCC-3') (central bp is underlined) and variants changing the central bp to A/T or swapping the flanking bp. The structures reveal a nearly two-fold widened minor groove in the central region of the DNA as compared to all other currently available NF-κB-DNA complex structures, which have a central A/T bp. Microsecond molecular dynamics (MD) simulations of free DNAs and p52 bound complexes reveal that free DNAs exhibit distinct preferred conformations, and p52:p52 homodimer induces the least amount of DNA conformational changes when bound to the more transcriptionally active natural G/C-centric PSel-κB, but adopts closed conformation when bound to the mutant A/T and swap DNAs due to their narrowed minor grooves. Our binding assays further demonstrate that the fast kinetics favored by entropy is correlated with higher transcriptional activity. Overall, our studies have revealed a novel conformation for κB DNA in complex with NF-κB and pinpoint the importance of binding kinetics, dictated by DNA conformational and dynamic states, in controlling transcriptional activation for NF-κB.

The Enigmatic Nature of the TCR-pMHC Interaction: Implications for CAR-T and TCR-T Engineering

The interaction of the T-cell receptor (TCR) with a peptide in the major histocompatibility complex (pMHC) plays a central role in the adaptive immunity of higher chordates. Due to the high specificity and sensitivity of this process, the immune system quickly recognizes and efficiently responds to the appearance of foreign and altered self-antigens. This is important for ensuring anti-infectious and antitumor immunity, in addition to maintaining self-tolerance. The most common parameter used for assessing the specificity of TCR-pMHC interaction is affinity. This thermodynamic characteristic is widely used not only in various theoretical aspects, but also in practice, for example, in the engineering of various T-cell products with a chimeric (CAR-T) or artificial (TCR-engineered T-cell) antigen receptor. However, increasing data reveal the fact that, in addition to the thermodynamic component, the specificity of antigen recognition is based on the kinetics and mechanics of the process, having even greater influence on the selectivity of the process and T lymphocyte activation than affinity. Therefore, the kinetic and mechanical aspects of antigen recognition should be taken into account when designing artificial antigen receptors, especially those that recognize antigens in the MHC complex. This review describes the current understanding of the nature of the TCR-pMHC interaction, in addition to the thermodynamic, kinetic, and mechanical principles underlying the specificity and high sensitivity of this interaction.

Amyloidogenesis: What Do We Know So Far?

The study of protein aggregation, and amyloidosis in particular, has gained considerable interest in recent times. Several neurodegenerative diseases, such as Alzheimer's (AD) and Parkinson's (PD) show a characteristic buildup of proteinaceous aggregates in several organs, especially the brain. Despite the enormous upsurge in research articles in this arena, it would not be incorrect to say that we still lack a crystal-clear idea surrounding these notorious aggregates. In this review, we attempt to present a holistic picture on protein aggregation and amyloids in particular. Using a chronological order of discoveries, we present the case of amyloids right from the onset of their discovery, various biophysical techniques, including analysis of the structure, the mechanisms and kinetics of the formation of amyloids. We have discussed important questions on whether aggregation and amyloidosis are restricted to a subset of specific proteins or more broadly influenced by the biophysiochemical and cellular environment. The therapeutic strategies and the significant failure rate of drugs in clinical trials pertaining to these neurodegenerative diseases have been also discussed at length. At a time when the COVID-19 pandemic has hit the globe hard, the review also discusses the plausibility of the far-reaching consequences posed by the virus, such as triggering early onset of amyloidosis. Finally, the application(s) of amyloids as useful biomaterials has also been discussed briefly in this review.

Impact of cancer evolution on immune surveillance and checkpoint inhibitor response

Intratumour heterogeneity (ITH) is pervasive across all cancers studied and may provide the evolving tumour multiple routes to escape immune surveillance. Immune checkpoint inhibitors (CPIs) are rapidly becoming standard of care for many cancers. Here, we discuss recent work investigating the influence of ITH on patient response to immune checkpoint inhibitor (CPI) therapy. At its simplest, ITH may confound the diagnostic accuracy of predictive biomarkers used to stratify patients for CPI therapy. Furthermore, ITH is fuelled by mechanisms of genetic instability that can both engage immune surveillance and drive immune evasion. A greater appreciation of the interplay between ITH and the immune system may hold the key to increasing the proportion of patients experiencing durable responses from CPI therapy.

Bispecific antibodies for immune cell retargeting against cancer

INTRODUCTION

Following the approval of the T-cell engaging bispecific antibody blinatumomab, immune cell retargeting with bispecific or multispecific antibodies has emerged as a promising cancer immunotherapy strategy, offering alternative mechanisms compared to immune checkpoint blockade. As we gain more understanding of the complex tumor microenvironment, rules and design principles have started to take shape on how to best harness the immune system to achieve optimal anti-tumor activities.

AREAS COVERED

In the present review, we aim to summarize the most recent advances and challenges in using bispecific antibodies for immune cell retargeting and to provide insights into various aspects of antibody engineering. Discussed herein are studies that highlight the importance of considering antibody engineering parameters, such as binding epitope, affinity, valency, and geometry to maximize the potency and mitigate the toxicity of T cell engagers. Beyond T cell engaging bispecifics, other bispecifics designed to recruit the innate immune system are also covered.

EXPERT OPINION

Diverse and innovative molecular designs of bispecific/multispecific antibodies have the potential to enhance the efficacy and safety of immune cell retargeting for the treatment of cancer. Whether or not clinical data support these different hypotheses, especially in solid tumor settings, remains to be seen.

Fluctuations in T cell receptor and pMHC interactions regulate T cell activation

Adaptive immune responses depend on interactions between T cell receptors (TCRs) and peptide major histocompatibility complex (pMHC) ligands located on the surface of T cells and antigen presenting cells (APCs), respectively. As TCRs and pMHCs are often only present at low copy numbers their interactions are inherently stochastic, yet the role of stochastic fluctuations on T cell function is unclear. Here, we introduce a minimal stochastic model of T cell activation that accounts for serial TCR-pMHC engagement, reversible TCR conformational change and TCR aggregation. Analysis of this model indicates that it is not the strength of binding between the T cell and the APC cell per se that elicits an immune response, but rather the information imparted to the T cell from the encounter, as assessed by the entropy rate of the TCR-pMHC binding dynamics. This view provides an information-theoretic interpretation of T cell activation that explains a range of experimental observations. Based on this analysis, we propose that effective T cell therapeutics may be enhanced by optimizing the inherent stochasticity of TCR-pMHC binding dynamics.

Downregulation of HLA class II is associated with relapse after allogeneic stem cell transplantation and alters recognition by antigen-specific T cells

Genomic deletion of donor-patient-mismatched HLA alleles in leukemic cells is a major cause of relapse after allogeneic hematopoietic stem cell transplantation (HSCT). Mismatched HLA is frequently lost as an individual allele or a whole region in HLA-class I, however, it is downregulated in HLA-class II. We hypothesized that there might be a difference in T cell recognition capacity against epitopes associated with HLA-class I and HLA-class II and consequently such allogeneic immune pressure induced HLA alterations in leukemic cells. To investigate this, we conducted in vitro experiments with T cell receptor-transduced T (TCR-T) cells. The cytotoxic activity of NY-ESO-1-specific TCR-T cells exhibited similarly against K562 cells with low HLA-A*02:01 expression. However, we demonstrated that the cytokine production against low HLA-DPB1*05:01 expression line decreased gradually from the HLA expression level approximately 2-log lower than normal expressors. Using sort-purified leukemia cells before and after HSCT, we applied the next-generation sequencing, and revealed that there were several marked downregulations of HLA-class II alleles which demonstrated consistently low expression from pre-transplantation. The marked downregulation of HLA-class II may lead to decreased antigen recognition ability of antigen-specific T cells and may be one of immune evasion mechanism associated with HLA-class II downregulation.

Hemozoin-mediated inflammasome activation limits long-lived anti-malarial immunity

During acute malaria, most individuals mount robust inflammatory responses that limit parasite burden. However, long-lived sterilizing anti-malarial memory responses are not efficiently induced, even following repeated Plasmodium exposures. Using multiple Plasmodium species, genetically modified parasites, and combinations of host genetic and pharmacologic approaches, we find that the deposition of the malarial pigment hemozoin directly limits the abundance and capacity of conventional type 1 dendritic cells to prime helper T cell responses. Hemozoin-induced dendritic cell dysfunction results in aberrant Plasmodium-specific CD4 T follicular helper cell differentiation, which constrains memory B cell and long-lived plasma cell formation. Mechanistically, we identify that dendritic cell-intrinsic NLRP3 inflammasome activation reduces conventional type 1 dendritic cell abundance, phagocytosis, and T cell priming functions in vivo. These data identify biological consequences of hemozoin deposition during malaria and highlight the capacity of the malarial pigment to program immune evasion during the earliest events following an initial Plasmodium exposure.

EGFR inhibitors, MHC expression and immune responses : Can EGFR inhibitors be used as immune response modifiers?

A recent study from our laboratory demonstrated that epidermal growth factor receptor (EGFR) inhibitors (EGFRIs) augment the expression of class I and class II MHC molecules. This finding provides an additional mechanism through which EGFRIs may exert anti-tumor effects and supports the notion that EGFRIs may influence adaptive immune responses by altering immune gene expression.

DNA origami demonstrate the unique stimulatory power of single pMHCs as T cell antigens

T cells detect with their T cell antigen receptors (TCRs) the presence of rare agonist peptide/MHC complexes (pMHCs) on the surface of antigen-presenting cells (APCs). How extracellular ligand binding triggers intracellular signaling is poorly understood, yet spatial antigen arrangement on the APC surface has been suggested to be a critical factor. To examine this, we engineered a biomimetic interface based on laterally mobile functionalized DNA origami platforms, which allow for nanoscale control over ligand distances without interfering with the cell-intrinsic dynamics of receptor clustering. When targeting TCRs via stably binding monovalent antibody fragments, we found the minimum signaling unit promoting efficient T cell activation to consist of two antibody-ligated TCRs within a distance of 20 nm. In contrast, transiently engaging antigenic pMHCs stimulated T cells robustly as well-isolated entities. These results identify pairs of antibody-bound TCRs as minimal receptor entities for effective TCR triggering yet validate the exceptional stimulatory potency of single isolated pMHC molecules.

Predicting Tumor Killing and T-Cell Activation by T-Cell Bispecific Antibodies as a Function of Target Expression: Combining In Vitro Experiments with Systems Modeling

Targeted T-cell redirection is a promising field in cancer immunotherapy. T-cell bispecific antibodies (TCB) are novel antibody constructs capable of binding simultaneously to T cells and tumor cells, allowing cross-linking and the formation of immunologic synapses. This in turn results in T-cell activation, expansion, and tumor killing. TCB activity depends on system-related properties such as tumor target antigen expression as well as antibody properties such as binding affinities to target and T cells. Here, we developed a systems model integrating in vitro data to elucidate further the mechanism of action and to quantify the cytotoxic effects as the relationship between targeted antigen expression and corresponding TCB activity. In the proposed model, we capture relevant processes, linking immune synapse formation to T-cell activation, expansion, and tumor killing for TCBs in vitro to differentiate the effect between tumor cells expressing high or low levels of the tumor antigen. We used cibisatamab, a TCB binding to carcinoembryonic antigen (CEA), to target different tumor cell lines with high and low CEA expression in vitro We developed a model to capture and predict our observations, as a learn-and-confirm cycle. Although full tumor killing and substantial T-cell activation was observed in high expressing tumor cells, the model correctly predicted partial tumor killing and minimal T-cell activation in low expressing tumor cells when exposed to cibisatamab. Furthermore, the model successfully predicted cytotoxicity across a wide range of tumor cell lines, spanning from very low to high CEA expression.

Relationship of 2D Affinity to T Cell Functional Outcomes

T cells are critical for a functioning adaptive immune response and a strong correlation exists between T cell responses and T cell receptor (TCR): peptide-loaded MHC (pMHC) binding. Studies that utilize pMHC tetramer, multimers, and assays of three-dimensional (3D) affinity have provided advancements in our understanding of T cell responses across different diseases. However, these technologies focus on higher affinity and avidity T cells while missing the lower affinity responders. Lower affinity TCRs in expanded polyclonal populations almost always constitute a significant proportion of the response with cells mediating different effector functions associated with variation in the proportion of high and low affinity T cells. Since lower affinity T cells expand and are functional, a fully inclusive view of T cell responses is required to accurately interpret the role of affinity for adaptive T cell immunity. For example, low affinity T cells are capable of inducing autoimmune disease and T cells with an intermediate affinity have been shown to exhibit an optimal anti-tumor response. Here, we focus on how affinity of the TCR may relate to T cell phenotype and provide examples where 2D affinity influences functional outcomes.

Modulation of Immune Responses to Influenza A Virus Vaccines by Natural Killer T Cells

Influenza A viruses (IAVs) circulate widely among different mammalian and avian hosts and sometimes give rise to zoonotic infections. Vaccination is a mainstay of IAV prevention and control. However, the efficacy of IAV vaccines is often suboptimal because of insufficient cross-protection among different IAV genotypes and subtypes as well as the inability to keep up with the rapid molecular evolution of IAV strains. Much attention is focused on improving IAV vaccine efficiency using adjuvants, which are substances that can modulate and enhance immune responses to co-administered antigens. The current review is focused on a non-traditional approach of adjuvanting IAV vaccines by therapeutically targeting the immunomodulatory functions of a rare population of innate-like T lymphocytes called invariant natural killer T (iNKT) cells. These cells bridge the innate and adaptive immune systems and are capable of stimulating a wide array of immune cells that enhance vaccine-mediated immune responses. Here we discuss the factors that influence the adjuvant effects of iNKT cells for influenza vaccines as well as the obstacles that must be overcome before this novel adjuvant approach can be considered for human or veterinary use.

A structure-kinetic relationship study using matched molecular pair analysis

The lifetime of a binary drug–target complex is increasingly acknowledged as an important parameter for drug efficacy and safety. With a better understanding of binding kinetics and better knowledge about kinetic parameter optimization, intentionally induced prolongation of the drug–target residence time through structural changes of the ligand could become feasible. In this study we assembled datasets from 21 publications and the K4DD (Kinetic for Drug Discovery) database to conduct large scale data analysis. This resulted in 3812 small molecules annotated to 78 different targets from five protein classes (GPCRs: 273, kinases: 3238, other enzymes: 240, HSPs: 160, ion channels: 45). Performing matched molecular pair (MMP) analysis to further investigate the structure–kinetic relationship (SKR) in this data collection allowed us to identify a fundamental contribution of a ligand's polarity to its association rate, and in selected cases, also to its dissociation rate. However, we furthermore observed that the destabilization of the transition state introduced by increased polarity is often accompanied by simultaneous destabilization of the ground state resulting in an unaffected or even worsened residence time. Supported by a set of case studies, we provide concepts on how to alter ligands in ways to trigger on-rates, off-rates, or both.

A large-scale study employing matched molecular pair (MMP) analysis to uncover the contribution of a compound's polarity to its association and dissociation rates.

The Quest for the Best: How TCR Affinity, Avidity, and Functional Avidity Affect TCR-Engineered T-Cell Antitumor Responses

Over the past decades, adoptive transfer of T cells has revolutionized cancer immunotherapy. In particular, T-cell receptor (TCR) engineering of T cells has marked important milestones in developing more precise and personalized cancer immunotherapies. However, to get the most benefit out of this approach, understanding the role that TCR affinity, avidity, and functional avidity play on how TCRs and T cells function in the context of tumor-associated antigen (TAA) recognition is vital to keep generating improved adoptive T-cell therapies. Aside from TCR-related parameters, other critical factors that govern T-cell activation are the effect of TCR co-receptors on TCR–peptide-major histocompatibility complex (pMHC) stabilization and TCR signaling, tumor epitope density, and TCR expression levels in TCR-engineered T cells. In this review, we describe the key aspects governing TCR specificity, T-cell activation, and how these concepts can be applied to cancer-specific TCR redirection of T cells.

Efficient Induction of Cytotoxic T Cells by Viral Vector Vaccination Requires STING-Dependent DC Functions

Modified Vaccinia virus Ankara (MVA) is an attenuated strain of vaccinia virus and currently under investigation as a promising vaccine vector against infectious diseases and cancer. MVA acquired mutations in host range and immunomodulatory genes, rendering the virus deficient for replication in most mammalian cells. MVA has a high safety profile and induces robust immune responses. However, the role of innate immune triggers for the induction of cytotoxic T cell responses after vaccination is incompletely understood. Stimulator of interferon genes (STING) is an adaptor protein which integrates signaling downstream of several DNA sensors and therefore mediates the induction of type I interferons and other cytokines or chemokines in response to various dsDNA viruses. Since the type I interferon response was entirely STING-dependent during MVA infection, we studied the effect of STING on primary and secondary cytotoxic T cell responses and memory T cell formation after MVA vaccination in STING KO mice. Moreover, we analyzed the impact of STING on the maturation of bone marrow-derived dendritic cells (BMDCs) and their functionality as antigen presenting cells for cytotoxic T cells during MVA infection in vitro. Our results show that STING has an impact on the antigen processing and presentation capacity of conventionel DCs and played a crucial role for DC maturation and type I interferon production. Importantly, STING was required for the induction of efficient cytotoxic T cell responses in vivo, since we observed significantly decreased short-lived effector and effector memory T cell responses after priming in STING KO mice. These findings indicate that STING probably integrates innate immune signaling downstream of different DNA sensors in DCs and shapes the cytotoxic T cell response via the DC maturation phenotype which strongly depends on type I interferons in this infection model. Understanding the detailed functions of innate immune triggers during MVA infection will contribute to the optimized design of MVA-based vaccines.

T cell stimulation and expansion by SunTag-based clustering of anti-CD3/CD28 scFv

Therapeutic ex vivo T cell expansion is limited by low rates and poor functionality, especially for T cells from aged cancer patients. Here, we describe a novel method for T cell stimulation and expansion using a system named SunTag-based clustering of anti-CD3/CD28 scFv (SBCS). In this method, SunTag was used to recruit up to 13 copies of anti-CD3/CD28 scFv for T cell activation. Compared with the traditional method using immobilized CD3/CD28 antibodies, the SBCS system produced approximately 1.5-fold greater expansion of T cells from healthy donors, and more than 2-fold greater expansion of T cells from aged cancer patients after stimulation. The efficiency of expansion depended mainly on the concentration of the clustered polymers of anti-CD3 scFv rather than anti-CD28 scFv. We also demonstrated that the SBCS-expanded T cells could be used to prepare functional chimeric antigen receptor modified T cells for antitumor therapy.

Manipulating the TCR signaling network for cellular immunotherapy: Challenges & opportunities

T cells can help confer protective immunity by eliminating infections and tumors or drive immunopathology by damaging host cells. Both outcomes require a series of steps from the activation of naïve T cells to their clonal expansion, differentiation and migration to tissue sites. In addition to specific recognition of the antigen via the T cell receptor (TCR), multiple accessory signals from costimulatory molecules, cytokines and metabolites also influence each step along the progression of the T cell response. Current efforts to modify effector T cell function in many clinical contexts focus on the latter - which encompass antigen-independent and broad, contextual regulators. Not surprisingly, such approaches are often accompanied by adverse events, as they also affect T cells not relevant to the specific treatment. In contrast, fine tuning T cell responses by precisely targeting antigen-specific TCR signals has the potential to radically alter therapeutic strategies in a focused manner. Development of such approaches, however, requires a better understanding of functioning of the TCR and the biochemical signaling network coupled to it. In this article, we review some of the recent advances which highlight important roles of TCR signals throughout the activation and differentiation of T cells during an immune response. We discuss how, an appreciation of specific signaling modalities and variant ligands that influence the function of the TCR has the potential to influence design principles for the next generation of pharmacologic and cellular therapies, especially in the context of tumor immunotherapies involving adoptive cell transfers.

TCR-Like CAR-T Cells Targeting MHC-Bound Minor Histocompatibility Antigens

Minor histocompatibility antigens (mHAgs) in allogeneic hematopoietic stem cell transplantation are highly immunogenic as they are foreign antigens and cause polymorphism between donors and recipients. Adoptive cell therapy with mHAg-specific T cells may be an effective option for therapy against recurring hematological malignancies following transplantation. Genetically modified T cells with T cell receptors (TCRs) specific to mHAgs have been developed, but formation of mispaired chimeric TCRs between endogenous and exogenous TCR chains may compromise their function. An alternative approach is the development of chimeric antigen receptor (CAR)-T cells with TCR-like specificity whose CAR transmembrane and intracellular domains do not compete with endogenous TCR for CD3 complexes and transmit their own activation signals. However, it has been shown that the recognition of low-density antigens by high-affinity CAR-T cells has poor sensitivity and specificity. This mini review focuses on the potential for and limitations of TCR-like CAR-T cells in targeting human leukocyte antigen-bound peptide antigens, based on their recognition mechanisms and their application in targeting mHAgs.

Rapid Assessment of Functional Avidity of Tumor-Specific T Cell Receptors Using an Antigen-Presenting Tumor Cell Line Electroporated with Full-Length Tumor Antigen mRNA

The functional avidity of T-cell receptor (TCR)-engineered T cells towards their cognate epitope plays a crucial role in successfully targeting and killing tumor cells expressing the tumor-associated antigen (TAA). When evaluating in vitro functional T-cell avidity, an important aspect that is often neglected is the antigen-presenting cell (APC) used in the assay. Cell-based models for antigen-presentation, such as tumor cell lines, represent a valid alternative to autologous APCs due to their availability, off-the-shelf capabilities, and the broad range of possibilities for modification via DNA or messenger RNA (mRNA) transfection. To find a valuable model APC for in vitro validation of TAA Wilms’ tumor 1 (WT1)-specific TCRs, we tested four different WT1 peptide-pulsed HLA-A2+ tumor cell lines commonly used in T-cell stimulation assays. We found the multiple myeloma cell line U266 to be a suitable model APC to evaluate differences in mean functional avidity (EC50) values of transgenic TCRs following transfection in 2D3 Jurkat T cells. Next, to assess the dose-dependent antigen-specific responsiveness of WT1 TCR-engineered 2D3 T cells to endogenously processed epitopes, we electroporated U266 cells with different amounts of full-length antigen WT1 mRNA. Finally, we analyzed the functional avidity of WT1 TCR-transfected primary CD8 T cells towards WT1 mRNA-electroporated U266 cells. In this study, we demonstrate that both the APC and the antigen loading method (peptide pulsing versus full-length mRNA transfection) to analyze T-cell functional avidity have a significant impact on the EC50 values of a given TCR. For rapid assessment of the functional avidity of a cloned TCR towards its endogenously processed MHC I-restricted epitope, we showcase that the TAA mRNA-transfected U266 cell line is a suitable and versatile model APC.

Adaptive threshold-stochastic resonance (AT-SR) in MHC clusters on the cell surface

Highly conserved 2D receptor clusters (membrane rafts) of immunological signaling molecules with MHCI and MHCII antigens as their cores have been observed in the past on the surface of T- and B-cell lines of lymphoid origin, as well as on cells from patients with colon tumor and Crohn's disease. Conservativity is related to the ever presence of MHCI molecules. Although they are suspected to play a role in maintaining these clusters and facilitating transmembrane signaling, their exact role has been left largely enigmatic. Here we are suggesting stochastic resonance (SR), or "noise-assisted signal detection", as a general organizing principle for transmembrane signaling events evoked by processes like immune recognition and cytokine binding taking place in these clusters. In the conceptual framework of SR, in immune recognition as a prototype of transmembrane signaling, the sea of self-peptide-MHC complexes around a nonself-peptide presenting MHC is conceived as a source of quickly fluctuating unspecific signal ("athermal noise") serving the extra energy for amplifying the weak sub-threshold specific signal of the nonself-peptide presenting MHC. This same noise is also utilized for a readjustment of the threshold - and also the sensitivity and specificity - of detection by a closed loop feedback control of the TcR-CD8 (CD4) proximity on the detecting T-cell. The weak sub threshold specific signal of nonself-peptide presenting MHC is amplified by the superposing unspecific signals of the neighboring self peptide-MHC complexes towards the T-cell receptor as the detector. Because in a successful detection event both self- and nonself-peptides are detected simultaneously, the principle of coincidence (or lock-in) detection is also realized. The ever presence of MHC islands gets a natural explanation as a source of extra power - in a form of "athermal noise" - needed for coincidence detection and frequency encoding the evoked downstream signals. The effect is quite general, because the actual type of molecules surrounding a chief signaling molecule - like nonself-peptide holding MHC, interleukin-2 and -15 cytokine receptors (IL-2R/15R) - as the fluctuating interaction energy sources is immaterial. The model applies also for other types of signaling, such as those evoked by cytokine binding. The phenomenon of SR can also be interpreted as sampling of a low frequency, specific signal with a high frequency unspecific signal, the "noise". Recipes for identifying other forms of SR in membrane clusters with biophysical tools are recommended.

Contribution of Resident Memory CD8+ T Cells to Protective Immunity Against Respiratory Syncytial Virus and Their Impact on Vaccine Design

Worldwide, human respiratory syncytial virus (RSV) is the most common etiological agent for acute lower respiratory tract infections (ALRI). RSV-ALRI is the major cause of hospital admissions in young children, and it can cause in-hospital deaths in children younger than six months old. Therefore, RSV remains one of the pathogens deemed most important for the generation of a vaccine. On the other hand, the effectiveness of a vaccine depends on the development of immunological memory against the pathogenic agent of interest. This memory is achieved by long-lived memory T cells, based on the establishment of an effective immune response to viral infections when subsequent exposures to the pathogen take place. Memory T cells can be classified into three subsets according to their expression of lymphoid homing receptors: central memory cells (T_CM), effector memory cells (T_EM) and resident memory T cells (T_RM). The latter subset consists of cells that are permanently found in non-lymphoid tissues and are capable of recognizing antigens and mounting an effective immune response at those sites. T_RM cells activate both innate and adaptive immune responses, thus establishing a robust and rapid response characterized by the production of large amounts of effector molecules. T_RM cells can also recognize antigenically unrelated pathogens and trigger an innate-like alarm with the recruitment of other immune cells. It is noteworthy that this rapid and effective immune response induced by T_RM cells make these cells an interesting aim in the design of vaccination strategies in order to establish T_RM cell populations to prevent respiratory infectious diseases. Here, we discuss the biogenesis of T_RM cells, their contribution to the resolution of respiratory viral infections and the induction of T_RM cells, which should be considered for the rational design of new vaccines against RSV.

Is TCR/pMHC Affinity a Good Estimate of the T-cell Response? An Answer Based on Predictions From 12 Phenotypic Models

On the T-cell surface the TCR is the only molecule that senses antigen, and the engagement of TCR with its specific antigenic peptide (agonist)/MHC complex (pMHC) is determined by the biochemical parameters of the TCR-pMHC interaction. This interaction is the keystone of the adaptive immune response by triggering intracellular signaling pathways that induce the expression of genes required for T cell-mediated effector functions, such as T cell proliferation, cytokine secretion and cytotoxicity. To study the TCR-pMHC interaction one of its properties most extensively analyzed has been TCR-pMHC affinity. However, and despite of intensive experimental research, the results obtained are far from conclusive. Here, to determine if TCR-pMHC affinity is a reliable parameter to characterize T-cell responses, a systematic study has been performed based on the predictions of 12 phenotypic models. This approach has the advantage that allow us to study the response of a given system as a function of only those parameters in which we are interested while other system parameters remain constant. A little surprising, only the simple occupancy model predicts a direct relationship between affinity and response so that an increase in affinity always leads to larger responses. Conversely, in the others more elaborate models this clear situation does not occur, i.e., that a general positive correlation between affinity and immune response does not exist. This is mainly because affinity values are given by the quotient k _on/k _off where k _on and k _off are the rate constants of the binding process (i.e., affinity is in fact the quotient of two parameters), so that different sets of these rate constants can give the same value of affinity. However, except in the occupancy model, the predicted T-cell responses depend on the individual values of k _on and k _off rather than on their quotient k _on/k _off. This allows: a) that systems with the same affinity can show quite different responses; and b) that systems with low affinity may exhibit larger responses than systems with higher affinities. This would make affinity a poor estimate of T-cell responses and, as a result, data correlations between affinity and immune response should be interpreted and used with caution.

Influence of ERAP1 and ERAP2 gene polymorphisms on disease susceptibility in different populations

The endoplasmic reticulum aminopeptidases (ERAPs), ERAP1 and ERAP2, makes a role in shaping the HLA class I peptidome by trimming peptides to the optimal size in MHC-class I-mediated antigen presentation and educating the immune system to differentiate between self-derived and foreign antigens. Association studies have shown that genetic variations in ERAP1 and ERAP2 genes increase susceptibility to autoimmune diseases, infectious diseases, and cancers. Both ERAP1 and ERAP2 genes exhibit diverse polymorphisms in different populations, which may influence their susceptibly to the aforementioned diseases. In this article, we review the distribution of ERAP1 and ERAP2 gene polymorphisms in various populations; discuss the risk or protective influence of these gene polymorphisms in autoimmune diseases, infectious diseases, and cancers; and highlight how ERAP genetic variations can influence disease associations.

How ERAP1 and ERAP2 Shape the Peptidomes of Disease-Associated MHC-I Proteins

Four inflammatory diseases are strongly associated with Major Histocompatibility Complex class I (MHC-I) molecules: birdshot chorioretinopathy (HLA-A^*29:02), ankylosing spondylitis (HLA-B^*27), Behçet's disease (HLA-B^*51), and psoriasis (HLA-C^*06:02). The endoplasmic reticulum aminopeptidases (ERAP) 1 and 2 are also risk factors for these diseases. Since both enzymes are involved in the final processing steps of MHC-I ligands it is reasonable to assume that MHC-I-bound peptides play a significant pathogenetic role. This review will mainly focus on recent studies concerning the effects of ERAP1 and ERAP2 polymorphism and expression on shaping the peptidome of disease-associated MHC-I molecules in live cells. These studies will be discussed in the context of the distinct mechanisms and substrate preferences of both enzymes, their different patterns of genetic association with various diseases, the role of polymorphisms determining changes in enzymatic activity or expression levels, and the distinct peptidomes of disease-associated MHC-I allotypes. ERAP1 and ERAP2 polymorphism and expression induce significant changes in multiple MHC-I-bound peptidomes. These changes are MHC allotype-specific and, without excluding a degree of functional inter-dependence between both enzymes, reflect largely separate roles in their processing of MHC-I ligands. The studies reviewed here provide a molecular basis for the distinct patterns of genetic association of ERAP1 and ERAP2 with disease and for the pathogenetic role of peptides. The allotype-dependent alterations induced on distinct peptidomes may explain that the joint association of both enzymes and unrelated MHC-I alleles influence different pathological outcomes.

Mathematical modeling identifies Lck as a potential mediator for PD-1 induced inhibition of early TCR signaling

Programmed cell death-1 (PD-1) is an inhibitory immune checkpoint receptor that negatively regulates the functioning of T cell. Although the direct targets of PD-1 were not identified, its inhibitory action on the TCR signaling pathway was known much earlier. Recent experiments suggest that the PD-1 inhibits the TCR and CD28 signaling pathways at a very early stage ─ at the level of phosphorylation of the cytoplasmic domain of TCR and CD28 receptors. Here, we develop a mathematical model to investigate the influence of inhibitory effect of PD-1 on the activation of early TCR and CD28 signaling molecules. Proposed model recaptures several quantitative experimental observations of PD-1 mediated inhibition. Model simulations show that PD-1 imposes a net inhibitory effect on the Lck kinase. Further, the inhibitory effect of PD-1 on the activation of TCR signaling molecules such as Zap70 and SLP76 is significantly enhanced by the PD-1 mediated inhibition of Lck. These results suggest a critical role for Lck as a mediator for PD-1 induced inhibition of TCR signaling network. Multi parametric sensitivity analysis explores the effect of parameter uncertainty on model simulations.

Antitumor activity of CAR-T cells targeting the intracellular oncoprotein WT1 can be enhanced by vaccination

The recent success of chimeric antigen receptor (CAR)-T cell therapy for treatment of hematologic malignancies supports further development of treatments for both liquid and solid tumors. However, expansion of CAR-T cell therapy is limited by the availability of surface antigens specific for the tumor while sparing normal cells. There is a rich diversity of tumor antigens from intracellularly expressed proteins that current and conventional CAR-T cells are unable to target. Furthermore, adoptively transferred T cells often suffer from exhaustion and insufficient expansion, in part, because of the immunosuppressive mechanisms operating in tumor-bearing hosts. Therefore, it is necessary to develop means to further activate and expand those CAR-T cells in vivo. The Wilms tumor 1 (WT1) is an intracellular oncogenic transcription factor that is an attractive target for cancer immunotherapy because of its overexpression in a wide range of leukemias and solid tumors, and a low level of expression in normal adult tissues. In the present study, we developed CAR-T cells consisting of a single chain variable fragment (scFv) specific to the WT1_235-243/HLA-A*2402 complex. The therapeutic efficacy of our CAR-T cells was demonstrated in a xenograft model, which was further enhanced by vaccination with dendritic cells (DCs) loaded with the corresponding antigen. This enhanced efficacy was mediated, at least partly, by the expansion and activation of CAR-T cells. CAR-T cells shown in the present study not only demonstrate the potential to expand the range of targets available to CAR-T cells, but also provide a proof of concept that efficacy of CAR-T cells targeting peptide/major histocompatibility complex can be boosted by vaccination.

COMPARISON OF A DUAL STRATEGY FOR T-CELL ACTIVATION UNDER INHIBITION OF THE CD4 RECEPTOR

We consider a stochastic model for T-cell activation proposed in Refs. [1] and [2] to compare the specificity and sensitivity of two different strategies for T-cell activation that utilize the history of phosphorylation of T-cell receptor (TCR). We compare these two strategies when the temporal signals/events that are essential for progressive T-cell activation are suppressed by blockade of CD4 receptor that may have caused by disease or therapeutic effects.3–6 We show that under these conditions, a threshold-strategy which is capable of maintaining a threshold (for total number of phosphorylated TCRs by time [Formula: see text]) for a further duration [Formula: see text] performs better in discriminating agonist peptides than a single-threshold strategy (reached by time [Formula: see text]) leading to T-cell activation using the Wentzell-Friedlin theory for large deviations for stochastic processes.7,8

Programmed self-assembly of peptide-major histocompatibility complex for antigen-specific immune modulation

A technology to prime desired populations of T cells in the body-particularly those that possess low avidity against target antigen-would pave the way for the design of new types of vaccination for intractable infectious diseases or cancer. Here, we report such a technology based on positive feedback-driven, programmed self-assembly of peptide-major histocompatibility complex (pMHC) directly on the membrane of cognate T cells. Our design capitalizes on the unique features of the protein annexin V (ANXA5), which-in a concerted and synergistic manner-couples the early onset of TCR signaling by cognate pMHC with a surge in pMHC-TCR affinity, with repeated pMHC encounters, and with widespread TCR cross-linking. In our system, ANXA5 is linked to pMHC and firmly engages the plasma membrane of cognate T cells upon (and only upon) the early onset of TCR signaling. ANXA5, in turn, exerts a mechanical force that stabilizes interactions at the TCR-pMHC interface and facilitates repeated, serial pMHC encounters. Furthermore, ANXA5 quickly arranges into uniform 2D matrices, thereby prompting TCR cross-linking. Fusion of ANXA5 to pMHC augments lymphocyte activation by several orders of magnitude (>1,000-fold), bypasses the need for costimulation, and breaks tolerance against a model self-antigen in vivo. Our study opens the door to the application of synthetic, feedback-driven self-assembly platforms in immune modulation.

Targeted Therapies: Immunologic Effects and Potential Applications Outside of Cancer

Two pharmacologic approaches that are currently at the forefront of treating advanced cancer are those that center on disrupting critical growth/survival signaling pathways within tumor cells (commonly referred to as "targeted therapies") and those that center on enhancing the capacity of a patient's immune system to mount an antitumor response (immunotherapy). Maximizing responses to both of these approaches requires an understanding of the oncogenic events present in a given patient's tumor and the nature of the tumor-immune microenvironment. Although these 2 modalities were developed and initially used independently, combination regimens are now being tested in clinical trials, underscoring the need to understand how targeted therapies influence immunologic events. Translational studies and preclinical models have demonstrated that targeted therapies can influence immune cell trafficking, the production of and response to chemokines and cytokines, antigen presentation, and other processes relevant to antitumor immunity and immune homeostasis. Moreover, because these and other effects of targeted therapies occur in nonmalignant cells, targeted therapies are being evaluated for use in applications outside of oncology.

Biomimetic Magnetosomes as Versatile Artificial Antigen-Presenting Cells to Potentiate T-Cell-Based Anticancer Therapy

Adoptive T-cell transfer for cancer therapy relies on both effective ex vivo T-cell expansion and in vivo targeting performance. One promising but challenging method for accomplishing this purpose is to construct multifunctional artificial antigen-presenting cells (aAPCs). We herein developed biomimetic magnetosomes as versatile aAPCs, wherein magnetic nanoclusters were coated with azide-engineered leucocyte membranes and then decorated with T-cell stimuli through copper-free click chemistry. These nano aAPCs not only exhibited high performance for antigen-specific cytotoxic T-cell (CTL) expansion and stimulation but also visually and effectively guided reinfused CTLs to tumor tissues through magnetic resonance imaging and magnetic control. The persisting T cells were able to delay tumor growth in a murine lymphoma model, while the systemic toxicity was not notable. These results together demonstrated the excellent potential of this "one-but-all" aAPC platform for T-cell-based anticancer immunotherapy.

Nanotechnology based therapeutic modality to boost anti-tumor immunity and collapse tumor defense

Cancer is still the leading cause of death. While traditional treatments such as surgery, chemotherapy and radiotherapy play dominating roles, recent breakthroughs in cancer immunotherapy indicate that the influence of immune system on cancer development is virtually beyond our expectation. Manipulating the immune system to fight against cancer has been thriving in recent years. Further understanding of tumor anatomy provides opportunities to put a brake on immunosuppression by overcoming tumor intrinsic resistance or modulating tumor microenvironment. Nanotechnology which provides versatile engineered approaches to enhance therapeutic effects may potentially contribute to the development of future cancer treatment modality. In this review, we will focus on the application of nanotechnology both in boosting anti-tumor immunity and collapsing tumor defense.

Modulation of Host Immunity by the Human Metapneumovirus

Globally, as a leading agent of acute respiratory tract infections in children <5 years of age and the elderly, the human metapneumovirus (HMPV) has gained considerable attention. As inferred from studies comparing vaccinated and experimentally infected mice, the acquired immune response elicited by this pathogen fails to efficiently clear the virus from the airways, which leads to an exaggerated inflammatory response and lung damage. Furthermore, after disease resolution, there is a poor development of T and B cell immunological memory, which is believed to promote reinfections and viral spread in the community. In this article, we discuss the molecular mechanisms that shape the interactions of HMPV with host tissues that lead to pulmonary pathology and to the development of adaptive immunity that fails to protect against natural infections by this virus.

T cell immunoengineering with advanced biomaterials

Recent advances in biomaterials design offer the potential to actively control immune cell activation and behaviour. Many human diseases, such as infections, cancer, and autoimmune disorders, are partly mediated by inappropriate or insufficient activation of the immune system. T cells play a central role in the host immune response to these diseases, and so constitute a promising cell type for manipulation. In vivo, T cells are stimulated by antigen presenting cells (APC), therefore to design immunoengineering biomaterials that control T cell behaviour, artificial interfaces that mimic the natural APC-T cell interaction are required. This review draws together research in the design and fabrication of such biomaterial interfaces, and highlights efforts to elucidate key parameters in T cell activation, such as substrate mechanical properties and spatial organization of receptors, illustrating how they can be manipulated by bioengineering approaches to alter T cell function.